Distribution and ecophysiology of the nitrifying bacteria emphasizing cultured species

Nitrification is an important factor in the global nitrogen cycle. Therefor e, an increasing number of publications deal with in situ studies of natura l bacterial populations participating in this process. However, some crucia l points complicate suchlike investigations. At the time being, a total of 25 species of ammonia-oxidizers and eight species of nitrite-oxidizers are cultured but the existence of many more species has been indicated by molec ular in situ investigations. With that, only a part of the existing nitrifi ers has been defined via isolation and subsequent physiological and molecul ar characterization. Furthermore, the distribution patterns of the distinct species of nitrifiers depend on various environmental parameters. Hence th e composition of nitrifying bacterial communities is complex and divers in heterogeneous habitats. In consequence of the above-mentioned problems, the representation of nitrifying community structures obtained from in situ in vestigations often has been incomplete and unbalanced in many respects. Pol yphasic approaches, applying a combination of classical as well as molecula r methods in parallel, could help to find the way for overcoming these prob lems in the future. Isolation and characterization of as many as possible n ew species seems to be one of the most important missing steps to advance a t this way. (C) 2001 Federation of European Microbiological Societies. Publ ished by Elsevier Science B.V. All rights reserved.